Atheroclerosis is a major cause of morbidity and mortality in insulin-resistant states such as metabolic[unreadable] syndrome and obesity. Defective regulation of macrophage lipid metabolism plays a central role in the[unreadable] development of vascular lesions associated with these dyslipidemic states. During atherogenesis,[unreadable] macrophages respond to the challenge of lipid excess through enzymatic production of oxysterols and[unreadable] activation of feed-forward nuclear receptor pathways that induce transcriptional programs involved in lipid[unreadable] uptake and efflux, and negatively regulate inflammatory responses. In recent studies, we have shown that[unreadable] the products of the Niemann-Pick type C (NPC) disease genes, NPC1 and NPC2, are required for delivery of[unreadable] lipoprotein-derived cholesterol to sites of intracellular oxysterol synthesis. In this proposal, we will test the[unreadable] hypothesis that macrophage-derived oxysterols play a critical role in the regulation of lipid[unreadable] homeostasis in the vascular wall. We propose that impaired synthesis of side-chain oxygenated sterols[unreadable] will reduce cholesterol efflux and increase cholesterol accumulation in macrophages, and, in concert with[unreadable] increased levels of oxidized cholesterol, promote cytotoxicity and lesion formation. Production of specific[unreadable] macrophage-derived cholesterol metabolites additionally may play a critical role in governing plasma[unreadable] lipoprotein levels through regulation of hepatic lipoprotein synthesis and/or clearance of plasma lipoproteins.[unreadable] This hypothesis will be tested by the following specific aims:[unreadable] 1) To determine whether macrophage-specific NPC1 and NPC2 loss of function alters macrophage oxysterol[unreadable] synthesis, thereby disrupting lipid homeostasis and promoting atherosclerosis in a murine model,[unreadable] 2) To determine whether macrophage-derived cholesterol metabolites affect regulation of plasma lipoprotein[unreadable] levels in chimeric mice with macrophage-specific NPC1 and NPC2 loss of function, and[unreadable] 3) To assess the relationship between plasma oxysterol levels and coronary heart disease and determine if[unreadable] oxysterol levels change following weight loss in humans with the metabolic syndrome.[unreadable] These studies will contribute to our understanding of the role of macrophage-derived cholesterol[unreadable] metabolites in atherogenesis and regulation of lipoprotein metabolism. This project has the potential to[unreadable] transform the care of people with the metabolic syndrome by establishing these metabolites as novel[unreadable] biomarkers for detection of subclinical atherosclerotic disease.